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Methods, systems, and apparatus, including computer programs encoded on a
computer storage medium for receiving, by a first device, a first signal
from a second device, the first signal including a carrier signal
modulated with a first modulation signal. Detecting a frequency of the
carrier signal by performing a carrier extraction (CAREX) process on the
first signal. Adding a second modulation signal to the carrier signal of
the first signal to produce a combined signal, wherein the second
modulation signal is a transpositional modulation (TM) signal and the
first modulation signal is a non-TM signal. Transmitting the combined
signal.

1. A device comprising: one or more processors; a receiver coupled to the
one or more processors; a transmitter coupled to the one or more
processors; and a data store coupled to the one or more processors having
instructions stored thereon which, when executed by the one or more
processors, causes the one or more processors to perform operations
comprising: receiving a first signal from a second device, the first
signal including a carrier signal modulated with a first modulation
signal; detecting a frequency of the carrier signal by performing a
carrier extraction (CAREX) process on the first signal; adding a second
modulation signal to the carrier signal of the first signal to produce a
combined signal, wherein the second modulation signal is a
transpositional modulation (TM) signal and the first modulation signal is
a non-TM signal; and transmitting the combined signal.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation application of U.S. patent
application Ser. No. 15/139,214, filed on Apr. 26, 2016, now U.S. Pat.
No. 9,628,318, which is hereby incorporated by reference in its entirety.

[0003] This specification relates to methods and systems for combining
transpositional modulation (TM) signals with traditional modulation
(non-TM) signals. More specifically, the specification relates to methods
and systems for receiving an existing non-TM signal and adding a TM
signal to the carrier of the non-TM signal with minimal or no
interference to the non-TM signal. In addition, the specification relates
to methods and systems for communications between devices using a
combined traditional modulation and TM signal on the same carrier signal.
Although discussed in the context of TM, implementations of the present
disclosure also may be applicable to other signal types.

[0004] In general, innovative aspects of the subject matter described in
this specification can be embodied in methods that include the actions of
receiving, by a first device, a first signal from a second device, the
first signal including a carrier signal modulated with a first modulation
signal. Detecting a frequency of the carrier signal by performing a
carrier extraction (CAREX) process on the first signal. Adding a second
modulation signal to the carrier signal of the first signal to produce a
combined signal, where the second modulation signal is a transpositional
modulation (TM) signal and the first modulation signal is a non-TM
signal. Transmitting the combined signal. Other implementations of this
aspect include corresponding systems, apparatus, and computer programs,
configured to perform the actions of the methods, encoded on computer
storage devices. These and other implementations can each optionally
include one or more of the following features.

[0005] Some implementations include synchronizing a phase of the combined
signal with a phase of the first signal.

[0006] In some implementations, adding the second modulation signal to the
carrier signal includes modulating a third harmonic signal of the carrier
signal of the first signal with data to produce the second modulation
signal, and combining the second modulation signal with the first signal.

[0007] In some implementations, adding the second modulation signal to the
carrier signal includes generating a second harmonic signal of the
carrier signal and a third harmonic signal of the carrier signal.
Modulating the third harmonic signal with a data signal. Mixing the
modulated third harmonic signal with the second harmonic signal to
produce the second modulation signal. And, combining the second
modulation signal with the first signal. Some implementations include
synchronizing a phase of the second modulation signal with a phase of the
first signal.

[0009] In some implementations, detecting a frequency of the carrier
signal includes detecting a center frequency of the first signal.
Detecting a frequency of a third signal. Determining a difference signal
between the center frequency of the first signal and the frequency of the
third signal. And, modifying the frequency of the third signal based on
the difference signal to provide the carrier signal.

[0010] In another general aspect, innovative aspects of the subject matter
described in this specification can be embodied in a communication device
that includes one or more processors, a receiver coupled to the one or
more processors, a transmitter coupled to the one or more processors, and
a data store coupled to the one or more processors. The data store
includes instructions stored thereon which, when executed by the one or
more processors, causes the one or more processors to perform operations
including receiving a first signal from a second device, the first signal
including a carrier signal modulated with a first modulation signal.
Detecting a frequency of the carrier signal by performing a CAREX process
on the first signal. Adding a second modulation signal to the carrier
signal of the first signal to produce a combined signal, where the second
modulation signal is a TM signal and the first modulation signal is a
non-TM signal. Transmitting the combined signal. This and other
implementations can each optionally include one or more of the following
features.

[0011] In some implementations, the device is a portable device. In some
implementations, the device includes a power source. In some
implementations, the power source can be one of a battery or a solar
power source.

[0012] Particular implementations of the subject matter described in this
specification can be implemented so as to realize one or more of the
following advantages. Implementations may increase the bandwidth of
signals transmitted using traditional modulation schemes. Implementations
may increase the data capacity for communication channels.
Implementations may permit the combination of two differently modulated
signals on a single carrier frequency. Some implementations may permit
extraction of carrier signals from a modulated signal with little or no a
priori information about the modulated signal. Some implementations may
be capable of extracting a carrier from a modulated signal without regard
to the type of modulation used in the modulated signal. In other words,
some implementations may able to extract carrier signals while being
agnostic to the type modulation of an input signal.

[0013] The details of one or more implementations of the subject matter
described in this specification are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages of the subject matter will become apparent from the
description, the drawings, and the claims.

[0022] FIGS. 7-9 depict example processes that can be executed in
accordance with implementations of the present disclosure.

[0023] Like reference numbers and designations in the various drawings
indicate like elements.

DETAILED DESCRIPTION

[0024] This specification relates to methods and systems for combining
transpositional modulation (TM) signals with traditional modulation
(non-TM) signals. More specifically, the specification relates to methods
and systems for receiving an existing non-TM signal and adding a TM
signal to the carrier of the non-TM signal with minimal or no
interference to the non-TM signal. In addition, the specification relates
to methods and systems for communications between devices using a
combined traditional modulation and TM signal on the same carrier signal.
Although discussed in the context of TM, implementations of the present
disclosure also may be applicable to other signal types.

[0025] Implementations of the present disclosure generally relate to
methods and systems for combining TM signals with traditional modulation
(non-TM) signals. More specifically, implementations provide methods and
systems for receiving an existing non-TM signal and adding a TM signal to
the carrier of the non-TM signal with minimal or no interference to the
non-TM signal. For example, an existing non-TM signal can be received by
a TM capable communication device. The communication device can extract
the carrier signal from the non-TM signal, modulate the extracted carrier
with additional data using a TM signal, and combine the TM signal with
the received non-TM signal with minimal or no interference to the non-TM
signal.

[0026] Other implementations of the present disclosure generally extract a
carrier signal from an existing modulated signal, modulate the extracted
carrier signal with a TM signal, and combine and retransmit the existing
signal with the TM signal on the same carrier signal. Specifically, the
implementations can extract a carrier frequency from a modulated signal
in which the carrier signal has been suppressed (e.g., QPSK, QAM, APSK,
BPSK). A CAREX (carrier extraction) circuit determines a frequency
difference between the frequency of the CAREX output signal and a
weighted average of the carrier frequency of the input signal. The
calculated difference value is used to continuously tune a signal
generator to maintain a minimal difference between the weighted average
of the input carrier frequency and the CAREX output. The third harmonic
of the extracted carrier is modulated with a data signal generating a TM
modulated signal. The TM modulated signal is heterodyned back to the
extracted carrier frequency and combined with the existing modulated
signal. The combined signal can then be transmitted. Moreover, the TM
modulated signal in the combined signal does not interfere with the
existing signal because the TM modulation is not recognized by
demodulation systems used to demodulate traditional modulation schemes.
Instead, the TM signal appears as a slight increase in noise within the
existing signal.

[0027] Other implementations of the present disclosure generally receive a
combined traditional modulation and TM signal on the same carrier signal
then separate the TM signal from the combined signal. Specifically, the
implementations can separate the existing signal from a combined signal
including a traditionally modulated signal (the existing signal) and a TM
modulated signal. The existing signal can be demodulated from the carrier
signal. An extracted carrier signal can be re-modulated with the
demodulated existing signal to re-create the existing signal alone,
absent the TM modulated signal. The re-modulated existing signal can be
removed from the combined signal leaving only the TM modulated signal
which can be demodulated using TM demodulation techniques described
herein.

[0028] As used herein the terms "Transpositional Modulation," "TM
modulation," "TM," and "TM signal" refer to a techniques of adding
information to a carrier signal without affecting the amplitude,
frequency or phase of the carrier signal (or a signal that is modulated
according to such a technique). More specifically, for example, the above
terms refer to a type of modulation in which information is conveyed by
altering (e.g., transposing, time shifting) a harmonic of a carrier
signal. For example, although the present disclosure is generally
directed to producing Transpostional Modulation by altering the third
harmonic of a carrier signal, in some implementations Transpostional
Modulation can be produced by altering other harmonics of a carrier
signal (e.g., a fourth harmonic, fifth harmonic, sixth harmonic, etc.).
Furthermore, Transpositional Modulation and/or TM signals are not
detectable by traditional de-modulators, for example, those used for
amplitude, frequency, or phase modulated signals.

[0029] FIG. 1A depicts an example system 100 in accordance with
implementations of the present disclosure. The system 100 is a system of
communication devices 102. The system 100 may be a radio frequency (RF)
communication system, a satellite communication system, a landline
communication system (e.g., a telephony or cable network), an optical
communication system, a computer network, or any other system of
communication devices 102. The communication devices 102 include systems
for modulating a carrier signal with an information signal using
traditional modulation techniques and transmitting and receiving the
modulated signal from one communication device 102 to/from another. For
example, communication device A may be a broadcast transmitter,
communication device B may be a signal repeater, and communication
devices C and D may be signal receives. Traditional modulation techniques
include, for example, amplitude modulation (AM), frequency modulation
(FM), and phase modulation (PM) in addition to complex modulation
techniques that incorporate aspects of AM, FM, and PM such as quadrature
phase shift keying (QPSK), amplitude phase shift keying (APSK) and
including quadrature amplitude modulation (QAM). In addition,
communication devices B and C include a TM transmitter 104 and a TM
receiver 106. In some examples, communication device C may be, for
example, a passive receiving device and may include a TM receiver 106 but
not a TM transmitter 104. In some examples, a TM transmitter 104 and/or a
TM receiver 106 can be integrated with traditional transmitters and
receivers. The TM transmitter 104 and/or TM receiver 106 can be
implemented as hardware devices (e.g., integrated circuits, chip-sets,
application specific integrated circuits (ASIC), or field programmable
logic arrays (FPGA)) or they can be implemented in software (e.g., as a
software defined radio (SDR)).

[0030] The system 100 can receive a traditionally modulated signal 108 and
combine the traditionally modulated signal 108 with a TM modulated signal
110 on the same carrier using a TM transmitter 104, thereby increasing
the overall bandwidth of the combined signal 112. The TM modulated signal
110 can be separated from the combined signal 112 and demodulated by a TM
receiver 106. Likewise, the traditionally modulated signal 108 can be
separately demodulated with no interference caused by the TM modulated
signal 110. This is possible because TM modulated signals are
undecipherable by non-TM receivers, instead appearing as a slight
increase of noise in traditionally modulated signals.

[0031] For example, communication device A may transmit a QAM signal 108
to communication device B. The TM transmitter 104 at communication device
B can receive the QAM signal 108 and extract the carrier signal from the
QAM signal 108. The TM transmitter 104 modulates the extracted carrier
signal with a TM signal, combines the TM modulated signal 110 with the
QAM signal 108, and retransmits the combined signal 112. In some
examples, as described below, the TM transmitter 104 can extract a
carrier signal from a traditionally modulated signal 108 (e.g., the QAM
signal) in which the carrier is suppressed and while having little or no
a priori information about the carrier signal (e.g., frequency or phase
information).

[0032] Communication devices C and D receive the combined signal 112. The
TM receiver 106 of communication device C separates and extracts the TM
modulated signal 110 from the combined signal 112, and then demodulates
the TM modulated signal 110 to obtain the TM modulated data signal. In
some examples, as described below, the TM receiver 106 separates the TM
modulated signal 110 from the combined signal 112 by demodulating
traditionally modulated signal 108 (e.g., the QAM signal), re-modulating
the carrier with only the traditionally modulated signal 108, and
subtracting the re-modulated carrier signal from the combined signal 112
leaving only the TM modulated signal 110. On the other hand,
communication device D, which does not have a TM receiver 106, will only
detect and demodulate the traditionally modulated signal 108; not the TM
modulated signal 110.

[0033] In some implementations, the carrier signal can be an intermediate
frequency (IF) carrier signal. That is, the carrier signal is not
necessarily at the same frequency of the carrier upon which the signal is
ultimately be transmitted, but may be at an IF used internally within a
system (e.g., a satellite communication system) as an intermediate step
in either signal transmission or reception. That is, in the case of
signal transmission, a system may up-convert a combined signal 112 from
the IF signal to a transmission carrier frequency prior to transmitting
the combined signal 112. Conversely, in the case of signal reception, a
system may down-convert a modulated signal from the transmission carrier
frequency to an IF frequency before separating the TM modulated signal
110 from the combined signal 112. In other implementations, an IF carrier
signal may not be used, and the transmission carrier signal can be
modulated with both a traditionally modulated signal and a TM modulated
signal.

[0034] FIG. 1B depicts an example environment 130 for employing the
techniques discussed above. The example environment is described in the
context of a communication network for emergency response services (e.g.,
police, fire department, medical service personnel responding to an
emergency situation such as a natural disaster). It is appreciated,
however, that implementations of the present disclosure can be realized
in other appropriate environments and contexts including, but not limited
to, for example, computer networks, broadcast networks, cablecast
networks, satellite systems, internet of things (IoT) networks, etc.

[0035] The environment 130 includes a broadcast signal source 132 (e.g., a
broadcast transmitter), a TM capable repeater station 134, and multiple
user communication devices 136a-136d, 138. The broadcast signal source
132 can be, for example, a transmitter that transmits a non-TM modulated
signal (e.g., such as communication device A of FIG. 1A). For example,
the broadcast signal source 132 can be an FM or AM radio transmitter, a
television transmitter, cablecast transmitter, a cellular service
transmitter, or a radio frequency (RF) communications transmitter (e.g.,
a high-frequency (HF) radio transmitter or repeater).

[0036] The user communication devices 136a-136d, 138 each include
receivers for receiving one or more types of non-TM modulated signals
from the broadcast signal source 134. For example, communication devices
136a-136d, 138 can include, AM, FM, or satellite radios, digital radios,
software radios (e.g., software defined radios (SDR)), smart phones,
tablet computers, televisions with broadcast or cablecast receivers,
citizen band (CB) radios, etc. Communication devices 136a-136b are
depicted as communication devices used by emergency service personnel.
For example, communication device 136a represents a radio system in an
emergency service vehicle. Communication device 136b represents a tablet
computer used by emergency service personnel. For example, communication
device 136b includes an SDR capable of receiving broadcast radio or
televisions signals. Communication devices 136c, 136d represent
communication systems in hospital or police dispatch centers or emergency
action centers. For example, communication devices 136c, 136d can include
broadcast/cablecast televisions systems, AM/FM/digital radio systems, and
dispatch radio systems. In addition, communication devices 136a-136c each
include a TM receiver (e.g., such as communication device C of FIG. 1A),
and, in some examples, a TM transmitter. Communication device 138 does
not include a TM receiver (e.g., such as communication device D of FIG.
1A) and represents a non-emergency services communication device (e.g.,
radio, television, smartphone, SDR, etc.).

[0037] The TM capable repeater station 134 includes both non-TM and TM
transmitters and receivers (e.g., such as communication device B of FIG.
1A). Repeater station 134 can receive non-TM broadcast signals 140,
create a combined signal 142 by adding TM signals to the same carrier as
the non-TM signal, and transmit the combined signals 142 for reception by
user communication devices 136a-136d, 138. As discussed above,
communication devices 136a-136d will be capable of detecting and
demodulating either or both the non-TM signals and the TM signals, while
communication device 138 will only be capable of detecting and
demodulating the non-TM signals.

[0038] The repeater station 134 can include, but is not limited to, a
mobile repeater station 134a, an aerial repeater station 134b, and a
fixed repeater station 134c. For example, a mobile repeater station 134a
can be transportable such that it can be readily deployed at a disaster
scene. In addition, a mobile repeater station 134a can include a local
power source (e.g., a battery, solar power source, a power generator).
For example, a mobile repeater station 134a can be implemented as a
handheld device, a "suitcase sized" device, or a truck/trailer
transportable device. The size of the mobile repeater station 134a may be
determined by the electronics required to obtain the desired transmission
power of the device and size of a power source required for the mobile
repeater station 134a. An aerial repeater station 134b can include a
repeater station that is attached to an aircraft or a drone. For example,
an aerial repeater station 134b can be deployable above a disaster area.
For example, a fixed repeater station 134c may be a primary entry point
(PEP) station for an emergency alert system (EAS).

[0039] For example, during an emergency, the repeater station 134 can
embed information for emergency services personnel into broadcast signals
140 from the broadcast signal source 132 using TM signals. The TM capable
communication devices 136a-136d used by the emergency services personnel
will be able to detect and receive the information in the TM signals, but
non-TM capable communication devices 138 will not.

[0040] For example, during a large scale disaster (e.g., an earthquake)
traditional communication channels can become overwhelmed and it may be
difficult to get much needed information to first responders and
dispatchers. When an emergency occurs, the TM capable repeater stations
134 can be used to provide additional communication channels for
emergency service personnel without affecting the normal media content
that is provided on existing channels (e.g. broadcast channels). For
example, a repeater station 134 that is setup in response to an emergency
can receive a broadcast signal 140 from a broadcast signal source 132.
For example, the broadcast signal 140 may be a radio station signal that
includes a normally scheduled radio program or a special news alert. The
repeater station 134 can add information for emergency service personnel
to the broadcast signal 140 without affecting the content contained in
the non-TM broadcast signal 140. For example, the information added to
the broadcast signal 140 can include but is not limited to, audio data,
image data, text data, and video data. Furthermore, the repeater station
134 can distribute information to coordinate first responders (e.g.,
deployment instructions, locations of disaster scenes, routing
information around blocked streets, etc.) and information to aid
dispatchers (e.g., on scene status reports, aerial images or video of
disaster scenes, e.g., from an aerial repeater station 134b) in the TM
signals.

[0041] In some implementations, a mobile repeater station 134a can be
setup at a disaster scene to distribute information from the scene. For
example, a mobile repeater station 134a can be setup at the site of a
collapsed roadway. The mobile repeater station 134a can be tuned to a
local FM radio station (a broadcast signal 140). On site personnel 146
can use the mobile repeater station 134a to transmit images from the
scene to a nearby dispatch center (e.g., a communication device 136c at a
hospital and/or fire station) and to EMS teams (e.g., communication
devices 136a, 136b) that are enroute to the scene. For example, the
mobile repeater station 134a can receive data for transmission in TM
signals from a communication device 144 at the scene. On site personnel
146 can capture images and/or video of the scene with a communicating
device 144 (e.g., a smartphone or tablet computer) and transfer the
images and/or video to the repeater station 134a. Communications between
the on scene communication device 144 and the repeater station 134a need
not use TM modulation, but can be accomplished using either non-TM signal
or TM signals. Furthermore, the communications between the on scene
communication device 144 and the repeater station 134a can be wired or
wireless. The repeater station 134a receives the data (e.g., images
and/or video) from the on scene communication device 144 and encodes the
data in a TM signal that is added to FM radio station broadcast signal
140 to create a combined signal 142. The repeater station 134a then
transmits the combined signal 142.

[0042] Each of the communication devices 136a-136d, 138 may receive the
combined signal 142, but only TM capable communication devices 136a-136d
will be able to detect and demodulate the TM portion of the combined
signal 142. For example, the communication device 138, which is not TM
capable, tuned to receive the broadcast signal 140 will detect only the
broadcast signal 140 included in the combined signal 142. Thus, the TM
signal containing information from the first responders will not affect
the music or news report that a driver is listening to on communication
device 138 (e.g., a car radio). At the same time, communication device
136c (e.g., a dispatch system at a hospital) will be able to detect and
demodulate the TM portion of the combined signal 142. Thus, hospital
personnel will be able to receive and view the images from the disaster
scene. The hospital personnel can then, for example, make more informed
decisions as to the type and extent of injuries that the first responders
are dealing with. This information can also be used to aid in determining
the number of additional first responders needed, the type of equipment
needed, and how to prepare the hospital to receive the influx of
patients. Moreover, such on scene information can be received from
multiple mobile repeater devices 134a at multiple disaster scenes to help
prioritize medical resources.

[0043] In another example implementation, an aerial repeater station 134b
can be flown over a disaster scene and/or surrounding areas. As with the
mobile repeater station 134a, the aerial repeater station 134b can be
tuned to a local FM radio station (a broadcast signal 140). The aerial
repeater station 134b can capture areal images or video of the scene for
transmission in the TM portion of a combined signal 142. For example, the
repeater station 134b can receive the aerial data (e.g., images and/or
video) from a camera on the aircraft and encode the data in a TM signal
that is added to FM radio station broadcast signal 140 to create a
combined signal 142. The repeater station 134b then transmits the
combined signal 142. As noted above, each of the communication devices
136a-136d, 138 may receive the combined signal 142, but only TM capable
communication devices 136a-136d will be able to detect and demodulate the
TM portion of the combined signal 142.

[0044] In another example implementation, a fixed repeater station 134c
can be used to send information to emergency service personnel. For
example, a fixed repeater station 134c can be used in a manner similar to
that discussed above in reference to the mobile repeater station 134a.
For example, a fixed repeater station 134c can be tuned to a radio or
television station that is transmitting an emergency broadcast signal 140
(e.g., an Emergency Alert System (EAS) message). The fixed repeater
station 134c can receive additional information for emergency service
personnel and encode the information for the emergency service personnel
in a TM signal to be transmitted in a combined signal 142 along with the
emergency broadcast signal 140. Communication devices 136c, 136d (e.g.,
televisions used in hospitals, fire stations, and police stations) can be
equipped to detect and decode the TM signals. Thus, when an emergency
broadcast signal is received such communication devices 136c, 136d can
display not only the emergency broadcast signal 140 but also information
pertinent to the emergency service personnel. For example, dispatch
orders or blocked routes to a disaster scene can be included in the TM
signals and presented to the emergency service personnel. In some
implementations, for example if the fixed repeater station 134c is a PEP
station for the EAS, the fixed repeater station 134c may not receive a
broadcast signal 140 from a separate broadcast signal source 132, but can
generate both the non-TM modulation signal for the emergency broadcast
signal and the TM modulation signal for the information specific to the
emergency service personnel. In other words, the fixed repeater station
134c may not add the TM signal to an existing non-TM broadcast signal,
but can generate and transmit both the non-TM and TM portions of the
combined signal 142.

[0045] FIG. 1C depicts another example environment 150 for employing the
techniques discussed above. The example environment is described in the
context of a communication network for a sports venue (e.g., a
racetrack). Again, it is appreciated that implementations of the present
disclosure can be realized in other appropriate environments and
contexts.

[0046] The environment 150 depicts several vehicles 152 each having
communication equipment (e.g., radios), pit crews 154 with pit crew
communication equipment 160, and race fans 156. In addition, the
environment 150 depicts a broadcast signal source 158 (e.g., a broadcast
transmitter). The broadcast signal source 158 can be, for example, a
transmitter that transmits a non-TM modulated signal (e.g., such as
communication device A of FIG. 1A). For example, the broadcast signal
source 158 can be an FM or AM radio transmitter broadcasting the race at
the race track.

[0047] In some implementations, a sports venue (e.g., racetrack, sports
stadium or arena) can use TM capable devices to provide fans with unique
entertainment experiences while watching a sporting event. For example, a
racetrack may provide fans 156 with the opportunity to listen to
communications 174 between their favorite driver and the driver's pit
crew. For example, fans 156a can rent a TM capable receiver device 161
for use at the racetrack. The pit crew's 154a communication equipment
160a can include a TM capable transmitter and receiver. In accordance
with the processes described above in reference to FIG. 1A, the
communication equipment 160a can add the communications 174 between the
driver of vehicle 152a and pit crew 154a to a broadcast signal 170 (e.g.,
a radio broadcast of the race). For example, the communication equipment
160a can encode the communications 174 in a TM signal and add the TM
signal to the broadcast signal 170 to produce combined signal 172.
Accordingly, only the TM capable receiver devices 161 will be able to
detect and demodulate the TM signals containing the driver/pit crew
communications 174. Thus, only fans 156a who rent the receiver devices
161 will be able to listen to the driver/pit crew communications 174.

[0048] In some examples, the TM capable receivers 161 can be implemented
as a mobile application for execution on the fans' 156a mobile device
(e.g., smartphone). For example, the TM capable receivers 161 can be
implemented as SDRs. In some examples, the broadcast signal 170 may be a
WiFi signal and the broadcast transmission source 158 can be WiFi access
points within the sports venue. In such implementations, the TM signals
including the driver/pit crew communications 174 can be added to the WiFi
signal. For example, the communication equipment 160 can add the TM
signals including the driver/pit crew communications 174 can be added to
the WiFi signal. In some examples, the WiFi access points can include TM
capable transmitters. For example, the driver/pit crew communications 174
can be sent through a computer network at the venue and the WiFi access
points can encode the communications 174 in a TM signal and add the TM
signal to the non-TM WiFi signals transmitted by the WiFi access point.

[0049] In another example implementation, a TM capable radio within a
vehicle 152b (e.g., racecar) can be used to add information associated
with the vehicle to the radio communications between the vehicle driver
and a pit crew 154b. For example, using the processes described above in
reference to FIG. 1A, a TM capable radio within a vehicle 152b can add a
TM signal including the vehicle information to the radio communication
signals 176 transmitted between the vehicle 152b and the pit crew's
communication equipment 160b. For example, a TM capable radio can add a
TM signal with vehicle diagnostic information to the carrier used for the
radio signals 176 to produce the combined signal 178. The communication
equipment 160b can also include a TM capable receiver to detect and
demodulate the TM signals. Accordingly, the vehicles diagnostic
information can be transmitted to the pit crew 154b without affecting the
radio communications signals 176. For example, the communication
equipment 160b can include a computer and a display for displaying the
diagnostic information to the pit crew 154b. Vehicle diagnostic
information can include, but is not limited to, engine data (e.g.,
temperatures, fluid levels, RPM), tire pressures, tire temperatures,
break temperatures, a video feed from the vehicle, etc.

[0051] FIG. 2 depicts a block diagram of an example TM signal transmitter
104 in accordance with implementations of the present disclosure. The TM
transmitter 104 includes a carrier extraction portion (CAREX 206), a
harmonic generation portion 202, a TM modulating portion 204, and a
heterodyning portion 205. The carrier extraction portion includes the
carrier extractor (CAREX) 206. The harmonic generation portion 202
includes a second harmonic generator 208 and a third harmonic generator
210. The TM modulating portion 204 includes a signal optimizer 212 and a
TM modulator 214. And, the heterodyning portion 205 includes a signal
mixer 216, a bandpass filter 218, and a power amplifier 220. In addition,
the TM transmitter 104 includes a signal coupler 222 and a signal
combiner 224.

[0052] In operation, the TM transmitter 104 receives an existing modulated
signal (e.g., traditionally modulated signal 108 of FIG. 1). The signal
coupler 222 samples the existing modulated signal and passes the sample
of the existing modulated signal to the CAREX 206. The CAREX 206 extracts
a carrier signal (f.sub.c) from the existing modulated signal. The CAREX
206 is described in more detail below in reference to FIGS. 3A-4B. The
output of the CAREX 206 is a pure sinusoidal signal at the fundamental
frequency of the carrier from the existing modulated signal. In some
examples, the CAREX 206 is agnostic to the type of modulation used in the
existing modulated signal. That is, the CAREX 206 can extract the carrier
signal from an existing modulated signal regardless of the type of
modulation used in the existing modulated signal. In some examples, the
CAREX 206 can extract carrier signals even when the carrier is suppressed
in the existing modulated signal, and can do so with little or no a
priori information about existing modulated signal's carrier (e.g.,
frequency or phase modulation information).

[0053] The CAREX 206 passes the extracted carrier signal to a second
harmonic signal generator 208 and a third harmonic signal generator 210,
which generate signals at the second and third harmonic frequencies
(2f.sub.c and 3f.sub.c respectively) of the fundamental carrier frequency
(f.sub.c). The second and third harmonic signals (2f.sub.c, 3f.sub.c) are
used by the TM modulation portion 204 and the heterodyning portion 205 of
the TM transmitter 104 to generate a TM modulated signal and to
heterodyne the TM modulated signal to the fundamental carrier frequency
(f.sub.c).

[0054] The TM modulation portion 204 of the TM transmitter 104 modulates
the third harmonic (3f.sub.c) of the carrier signal (f.sub.c) with a data
signal to generate the TM modulated signal. The TM modulated signal is
then heterodyned to the frequency of the carrier signal (f.sub.c),
combined with the existing modulated signal, and outputted to an antenna
for transmission.

[0055] In more detail, TM modulation portion 204 receives a data signal
for transmission (e.g., a baseband (BB) data signal). The data signal is
optionally processed for transmission as a TM modulated signal by the
signal optimizer 212. In some examples, the signal optimizer 212 produces
an optional pattern of inversion and non-inversion of the modulating
signal, and filters the modulating signal to ensure that the total
bandwidth of the data signal is within the channel bandwidth of the
existing modulated signal. In some examples, the signal optimizer 212 can
include sample-and-hold circuitry and filters to prepare the modulating
signal for transmission as a TM modulated signal. In some examples, the
signal optimizer 212 can be bypassed or turned off and on.

[0056] The TM modulator 214 modulates the third harmonic (3f.sub.c) of the
carrier signal (f.sub.c) with a data signal to generate the TM modulated
signal. For example, the TM modulator 214 modulates the third harmonic
(3f.sub.c) by introducing a variable time delay based on the data signal.
In other words, the TM modulator 214 can use the data signal as a control
signal for introducing an appropriate time delay to third harmonic
(3f.sub.c). As such, an amount of time delay introduced into the third
harmonic (3f.sub.c) represents discrete bits or symbols of the data
signal. The described time delay modulation technique may be considered
as time-shift modulation and is performed on the third harmonic
(3f.sub.c) of the intended carrier frequency (3f.sub.c).

[0057] The time-shift modulation of the third harmonic (3f.sub.c) produces
a single set of upper and lower Bessel-like sidebands. The inventor has
confirmed such results in laboratory simulations with an oscilloscope and
spectrum analyzer. Moreover, the bandwidth of these sidebands can be
limited to the bandwidth of an intended communication channel by the
optimizer 212 before TM modulation of the signal, as described above.

[0058] In some examples, the time delay may be a phase shift. However, the
time-shift modulation described above is not equivalent phase modulation.
As noted above, the inventor has confirmed in laboratory tests that the
time-shift modulation only produces a single pair of upper and lower
Bessel-like sidebands. Phase modulation, however, produces a series upper
and lower Bessel-like sidebands.

[0059] The heterodyning portion 205 prepares the TM modulation signal do
be combined with the existing modulated signal and transmitted by the
receiver. The TM modulated signal is then heterodyned (e.g., frequency
shifted) by mixer 216 down to the fundamental frequency of the carrier
signal (f.sub.c). The mixer 216 multiplies the TM modulated signal with
the second harmonic of the carrier (2f.sub.c) which shifts the TM
modulated signal to both the fundamental carrier signal frequency
(f.sub.c) and the fifth harmonic frequency of the carrier. The bandpass
filter 218 removes signal at the fifth harmonic frequency as well as any
additional signals or noise outside of the bandwidth of the TM modulated
signal centered at the fundamental carrier signal frequency (f.sub.c).

[0060] The TM modulated carrier signal is amplified by power amplifier 220
and combined with the existing modulated signal by the signal combiner
224. It may be necessary, in some examples, to adjust the phase of the TM
modulated carrier signal to match the phase of the carrier in the
existing modulated signal before combining the two signals and
transmitting the combined signal.

[0061] FIG. 3A depicts a block diagram of an example CAREX 206 in
accordance with implementations of the present disclosure. The CAREX 206
can be implemented as a circuit in a device such as a TM transmitter or
TM receiver, for example. In some implementations, the CAREX 206 can be
implemented as a standalone device for installation into in a larger
system (e.g., an application specific integrated circuit (ASIC) or field
programmable logic array (FPGA)). In some implementations, the CAREX 206
can be implemented in software, for example, as a set of instructions in
a computing device or a digital signal processor (DSP).

[0062] The CAREX 206 operates by determining a center frequency of an
input signal (e.g., either modulated or unmodulated), comparing the
center frequency to the frequency of a pure sinusoidal signal produced by
a signal generator to create a error signal, and adjusting the frequency
of the signal generator output signal based on a control signal generated
from the error signal until the error signal is minimized. Furthermore,
the CAREX 206 does not require a priori information about a carrier
signal to extract the carrier signal and can extract carrier signals when
the carrier of the modulated signal is suppressed.

[0063] The CAREX 206 includes amplitude limiters 302a, 302b, filters 304a,
304b, frequency detectors 306a, 306b, signal generator 308, difference
circuit 310, and an amplifier 312. The amplitude limiter 302a and filter
304a condition input signal before the input signal is analyzed by the
first frequency detector 306a. The amplitude limiter 302a removes any
variations in the amplitude of the input signal. In other words, the
amplitude limiter 302a stabilizes the amplitude of the input signal. In
some examples, the amplitude limiters 302a, 302b can be an analog
comparator or an automatic gain control (AGC) circuit. The filters 304a,
304b are bandpass filters and removes extraneous signals (e.g.,
harmonics) and noise outside the channel bandwidth of the input signal.

[0064] The frequency detectors 306a and 306b can be frequency
discriminators or quadrature detectors. The first frequency detector 306a
detects the center frequency of the input signal. As shown in the
frequency domain plot 320, an input signal produced by traditional
modulation techniques generally has symmetric sidebands 322 located on
either side of the carrier frequency 324. The frequency detector 306a can
determine a center frequency of an input signal based on, for example,
the frequencies of the outer edges of the sidebands 322. Furthermore, the
frequency detector 306a can use the sidebands 322 of an input signal to
determine the center frequency even if the carrier signal 324 is
suppressed, as illustrated by the dotted line.

[0065] The signal generator 308 generates a pure sinusoidal signal (e.g.,
a single frequency signal) which is provided to a second frequency
detector 306b. The signal generator 308 can be, for example, a voltage
controlled oscillator (VCO) such as, but not limited to, a voltage
controlled LC (inductor-capacitor) oscillator circuit, a voltage
controlled crystal oscillator (VCXO), or a temperature-compensated VCXO.
The second frequency detector 306b detects the frequency of the output
signal from the signal generator 308. In some examples, the output signal
from the signal generator 308 is provided to an amplitude limiter 302b
and filter 304b before being transmitted to the second frequency detector
306b. The amplitude limiter 302b and filter 304b stabilize and filter the
amplitude of the signal generator output signal similar to amplitude
limiter 302a and filter 304a.

[0066] The output from each of the first and second frequency detectors
306a, 306b is provided as inputs to the differencing circuit 310. The
output of both the first and second frequency detectors 306a, 306b can
be, in some examples, a direct current (DC) voltage signal representing
the center frequency of the input signal and the frequency of the signal
generator 308 output signal, respectively. The output of the difference
circuit 310 is a error signal representing the difference in frequency
between the center frequency of the input signal in the signal generator
output signal. The error signal (e.g., a DC voltage) is amplified by
amplifier 312 and provided as a control signal to the signal generator
308. The amplifier 312 can be, for example, a high gain integrating
circuit that integrates the inputted error signal over time to produce
the control signal.

[0067] The signal generator 308 adjusts the frequency of its output signal
based on the control signal until the frequency of the signal generator
308 output is matched to the center frequency of the input signal. The DC
value of the control signal is used to control the frequency of the
signal generator output, as shown in FIG. 4B and described below. The
signal generator output is provided as the output of the CAREX 206.
Frequency domain plot 330 and time domain plot 334 represent an example
CAREX 206 output signal. As shown, the output signal of the CAREX 206 is
a pure sinusoidal signal having a frequency 332 equivalent to the
fundamental carrier frequency of the input signal.

[0068] In some implementations, the frequency detectors 306a and 306b are
matched. In some examples, the matched frequency detectors 306a and 306b
have similar frequency to DC output characteristics over changing
modulated input frequencies. In some examples, the matched frequency
detectors 306a and 306b have similar thermal and aging properties. In
some examples, the amplitude limiters 302a and 302b, and the filters 304a
and 304b are matched.

[0069] In some examples, when the error signal is minimized the signal
generator output is effectively matched to the center frequency of the
input signal. For example, the error signal can be considered as
minimized when its magnitude is zero or substantially close to zero
(e.g., when the control signal has a magnitude that is negligible in
relation signal magnitudes measureable or usable by components of the
CAREX 206). In some examples, the error signal is considered to be
minimized when its magnitude is below a threshold value (e.g., an error
tolerance threshold).

[0070] In some implementations, the CAREX 206 is adapted to extract
carrier frequencies from single sideband signals. In some examples, the
CAREX 206 includes a controller that offsets the output signal of the
signal generator 308 by an appropriate offset frequency. For example, the
output of the frequency generator 308 can be offset after it is fed back
to the second frequency detector 306b, so as to not adversely affect the
control signal. In some examples, the first frequency detector 306a can
be configured to determine a frequency offset based on the bandwidth of
the input signal. In such examples, the first frequency detector 306a can
adjust the detected frequency by the frequency offset.

[0071] FIG. 3B is a block diagram of an example frequency detector 306 in
accordance with implementations of the present disclosure. The frequency
detector 306 illustrated in FIG. 3B is an example quadrature-based
detector circuit. The frequency detector 306 includes a phase shift
network 350, a signal mixer 352, and a filter 354. The phase shift
network 350 is a frequency sensitive circuit, such as an all pass filter,
for example, that causes a phase shift in an input signal that
corresponds with the frequency of the input signal. In other words, the
phase shift network 350 causes a change in the phase angle of the input
signal relative to the frequency of the input signal. In some examples,
the phase shift network 350 is tuned to produce a nominal phase shift of
90 degrees (e.g., quadrature to the input signal) for a nominal design
frequency (e.g., a 70 MHz IF for a communication system).

[0072] The signal mixer 352 can be, for example, a signal multiplier. The
signal mixer 352 receives the input signal and an output signal from the
phase shift network 350 as inputs. The filter 354 is a low pass filter.

[0073] Plot 360 shows example signals at various points in the frequency
detector 306. The input signal (Signal A) is passed to the phase shift
network 350 and the signal mixer 352. Signal A is shown as a sinusoid for
simplicity, however, Signal A can be a modulated signal. Signal B is the
output of the phase shift network 350 and is phase shifted relative to
the input signal (Signal A). The value of the phase shift corresponds to
the frequency of Signal A, and is nominally 90 degrees for a design
frequency. Deviations from the design frequency resulting in a phase
shift of Signal B that deviates from the nominal 90 degrees. The input
signal (Signal A) is mixed with the output of the phase shift network 350
(Signal B) to produce Signal C (e.g., Signal C=Signal A.times.Signal B).
Signal C has a DC offset component corresponding to the phase difference
between Signals A and B, and by extension, to the frequency of Signal A.
The low pass filter 354 then removes the high frequency components of
Signal C leaving only the DC component (Signal D). The deviation of
Signal B's phase shift from the a nominal 90 degrees is exaggerated in
plot 360 in order to clearly show the resulting DC output signal (Signal
D).

[0074] FIG. 4A depicts a plot 400 of an example control signal 402
generated in an example CAREX 206. The plotted control signal 402 is an
example of the input signal to the signal generator 308 of FIG. 3A. The
plotted control signal 452 is broken into several regions (406-410). The
regions illustrate a variations 404 in the control signal 402 as the
input signal to the CAREX 206 is switched between several different input
signals, each modulated using a different type of modulation. The input
signal in region 406 is a QPSK modulated signal. The input signal in
region 408 is a QAM modulated signal. The input signal in region 410 is
an unmodulated carrier signal. Each of the input signals in regions
406-410 is applied to a 70 MHz carrier. The plot 400 illustrates the
robustness of the CAREX 206 and its adaptability to extracting carrier
signals from various input signals without regard to the types of
modulation applied to the carrier signal.

[0075] FIG. 4B depicts a plot 450 of another example control signal 452
generated in an example CAREX 206. The plotted control signal 452 is an
example of the input signal to the signal generator 308 of FIG. 3A. The
plotted control signal 452 is broken into several regions (456-460). The
regions illustrate transitions 454 of the control signal 452 as the input
signal to the CAREX 206 is switched between several different input
signals, each having a different carrier frequency. The input signal in
region 456 is a 67 MHz carrier signal. The input signal in region 458 is
a 73 MHz carrier signal. The input signal in region 460 is a 70 MHz
carrier signal. The plot 450 illustrates the robustness of the CAREX 206
and its adaptability to extracting different frequency carrier signals.
In some implementations, as shown, the CAREX 206 loop can be designed for
a specific center frequency (e.g., 70 MHz as shown). For example, the
design center frequency can be a specific carrier frequency or IF of a
communication system such as a satellite or radio frequency (RF)
communication system, for example.

[0076] FIG. 5 depicts a block diagram of an example TM signal receiver 106
in accordance with implementations of the present disclosure. The TM
receiver 106 includes a carrier extraction portion (e.g., CAREX 506), a
harmonic generation portion 504, a signal separation and extraction
portion (SEPEX) device 512, and a TM demodulator 514. As in the TM
transmitter 104, the harmonic generation portion includes a second
harmonic generator 508 and a third harmonic generator 510. In addition,
the TM receiver 106 can include a signal splitter 502 to split a combined
input signal (e.g. combined signal 112 of FIG. 1) between the TM receiver
106 and a signal receiver for traditional modulated signals.

[0077] In operation, the TM receiver 106 receives a combined input signal
and provides the combined signal to both the CAREX 506 and SEPEX device
512. As described above in reference to the TM receiver 106, the CAREX
506 extracts a carrier signal (f.sub.c) from the combined signal, and the
second harmonic generator 508 and third harmonic generator 510,
respectively, generate second and third harmonics (2f.sub.c and 3f.sub.c)
of the extracted fundamental carrier frequency (f.sub.c). Both the
carrier signal (f.sub.c) and second harmonic signal (2f.sub.c) are
provided to the SEPEX device 512. The third harmonic signal (3f.sub.c) is
provided to the TM demodulator 514.

[0078] The TM demodulation portion 504 separates and extracts the
traditionally modulated signal from the combined signal to obtain the TM
modulated signal. The SEPEX device 512 provides the TM modulated signal
to the TM demodulator 514, which, demodulates the TM modulated signal to
obtain a baseband data signal. The SEPEX device 512 separates and
extracts the TM modulated signal from the combined signal. In some
implementations, before outputting the TM modulated signal, the SEPEX
device 512 heterodynes (e.g., up-shifts) the TM modulated signal to the
third harmonic frequency (3f.sub.c) for demodulation. The SEPEX device
512 is described in more detail below in reference to FIG. 6.

[0079] The TM demodulator 514 uses the third harmonic signal (3f.sub.c)
provided by the third harmonic generator 210 as a reference signal for TM
demodulation. The TM demodulator 514 demodulates the TM signal by sensing
the time shifts between TM modulated carrier signal from the SEPEX device
512 and the third harmonic signal (3f.sub.c). In some examples, the TM
demodulator 514 can be a phase detection circuit. In some
implementations, the TM demodulator 514 detects the time shifts by
determining a correlation between the TM modulated carrier signal and the
third harmonic signal (3f.sub.c) based on, for example, a product of the
two signals.

[0080] FIG. 6A depicts a block diagram of an example TM signal SEPEX
device 512 in accordance with implementations of the present disclosure.
The SEPEX device 512 can be implemented as a circuit in a device such as
a TM receiver, for example. In some implementations, the SEPEX device 512
can be implemented as a standalone device for installation into in a
larger system (e.g., an application specific integrated circuit (ASIC) or
field programmable logic array (FPGA)). In some implementations, the
SEPEX device 512 can be implemented in software, for example, as a set of
instructions in a computing device or a digital signal processor (DSP).

[0081] In operation, the SEPEX device 512 demodulates the traditionally
modulated signal from the combined signal. Because the TM modulation is
not detected by traditional signal demodulation, the resulting signal
does not include the TM signal, but only the demodulated data signal from
the traditional modulation signal. A "clean" (e.g., un-modulated) carrier
is then re-modulated with the previously demodulated data signal from the
traditional modulation signal. The SEPEX 512 computes the difference
between the combined signal and the re-modulated signal to obtain a TM
modulated carrier signal. In other words, the SEPEX device 512 removes a
traditionally modulated signal from the combined signal by demodulating
the traditionally modulated signal, re-modulating a "clean" (e.g.,
un-modulated) carrier, and subtracting the re-modulated signal from the
combined signal, thereby, leaving only the TM modulated carrier.

[0082] The SEPEX device 512 includes a signal demodulator 602, a signal
modulator 604, low-pass filters 606a, 606b, a summing circuit 608, a
difference circuit 610, a delay circuit 612, a mixer 614, a bandpass
filter 616, and an amplitude limiter 618. The demodulator 602 is a non-TM
signal demodulator, and the modulator 604 is a non-TM signal modulator.
That is, the demodulator 602 and modulator 604 are traditional modulation
type (e.g., AM, FM, PM, QAM, APSK, etc.) demodulator and modulator. The
demodulator 602 and modulator 604 are depicted as a complex (e.g.,
quadrature and in-phase) demodulator and modulator, however, in some
examples the demodulator 602 and modulator 604 can be a simple (e.g.,
single phase) demodulator and modulator.

[0083] The operation the SEPEX device 512 is described below in more
detail and with reference to FIGS. 6A and 6B. FIG. 6B depicts frequency
domain representations of signals (A-F) at various stages of the SEPEX
device 512. The demodulator 602 receives the combined signal (A) (e.g.
combined signal 112 of FIG. 1) as one input, and the carrier signal
(f.sub.c) from the CAREX 506 as a second input. The combined signal
includes both a traditionally modulated signal and a TM modulated signal.
As shown by signal (A) in FIG. 6B, the combined signal includes frequency
content from both the TM modulated signal and the traditionally modulated
signal centered about the carrier frequency (f.sub.c). The demodulator
602 demodulates the traditional modulated signal from the combined signal
producing a baseband data signal. As noted above, because the TM
modulation is not detected by traditional signal demodulation, the
resulting baseband data signal does not include a TM signal.

[0084] In the case of complex modulation, the demodulator 602 demodulates
both the in-phase and quadrature phase of the combined signal producing
an in-phase and a quadrature phase baseband data signal. The low-pass
filters 606a and 606b remove any extraneous signals or noise from the
baseband data signals, for example, harmonics introduced by the
demodulation process. The resulting baseband data signal, shown by signal
(B), includes only the frequency content from the traditionally modulated
signal centered at zero frequency (baseband). More specifically, a TM
modulated signal does not exist at baseband, and thus, the TM modulated
signal is removed by converting the traditionally modulated signal to
baseband.

[0085] The modulator 604 receives the baseband data signals (e.g.,
in-phase and quadrature phase signals) as a first input, and the carrier
signal (f.sub.c) from the CAREX 506 as a second input. The modulator 604
re-modulates the un-modulated carrier signal (f.sub.c) from the CAREX 506
with the baseband data signals resulting in re-modulated carriers
(re-modulated in-phase and quadrature phase carriers) having only the
traditionally modulated signal. The in-phase and quadrature phase
re-modulated carriers are combined by the summing circuit 608 (signal
(C)). FIG. 6B signal (C) shows the re-modulated signal again centered
about the carrier frequency (f.sub.c). In some examples, the carrier
signal (f.sub.c) may be phase shifted or delayed to account for delays
introduced into the baseband data signals during the demodulation and
filtering process. This is to ensure that the resulting re-modulated
signal is in phase with the combined signal.

[0086] The re-modulated signal is subtracted from the combined signal by
the difference circuit 610 removing the traditionally modulated signal
from the combined signal. The resulting signal, show by signal (D),
includes only the TM modulated carrier signal (f.sub.c). The combined
signal is delayed by the delay circuit 612 to account for delays
introduced into the re-modulated signal by the demodulation and
re-modulation process.

[0087] The TM modulated signal is heterodyned (e.g., up-shifted) to the
third harmonic (3fc) by the mixer 614. The mixer 614 multiplies the TM
modulated signal with the second harmonic (2f.sub.c) of the carrier from
the second harmonic generator 508 producing signal (E). Heterodyning the
TM modulated carrier signal (f.sub.c) with the second harmonic (2fc)
shifts the TM modulated signal to both the third harmonic (3fc) and the
negative carrier frequency (-fc) (e.g., a phase inverted version of the
TM modulated signal at the carrier frequency). The bandpass filter 616
removes the phase inverted TM signal at the carrier frequency leaving
only the TM modulated third harmonic (3fc) (signal (F)), and the optional
amplitude limiter 618 removes any variations in the amplitude of the TM
modulated third harmonic signal.

[0088] In some examples, the SEPEX device 512 can include multiple
different types of demodulators 602 and modulators 604. For example, the
SEPEX device 512 can include FM, PM, and QAM demodulators 602 and
modulators 604. In such examples, the SEPEX device 512 can also include a
control device that detects the type of traditional modulation on input
signal, and sends the input signal to the appropriate set of demodulator
and modulator.

[0089] Although the SEPEX device 512 is described in the context of
separating and extracting a TM modulated signal from a traditionally
modulated signal, in some implementations, the SEPEX device 512 can be
modified to separate two traditionally modulated signals such as
separating non-quadrature modulated signals (e.g., in-phase modulated
signal) and quadrature modulated signals. For example, a non-quadrature
modulated signal could be separated and extracted from a combined I/Q
modulated signal by modifying the SEPEX device 512 shown in FIG. 6A such
that only the quadrature modulated signal is demodulated and demodulated
by demodulator 602 and modulator 604.

[0090] FIG. 7 depicts an example process 700 for adding information to
existing communication signals that can be executed in accordance with
implementations of the present disclosure. In some examples, the example
process 700 can be provided as computer-executable instructions executed
using one or more processing devices (e.g., a digital signal processor)
or computing devices. In some examples, the process 700 may be hardwired
electrical circuitry, for example, as an ASIC or an FPGA device. In some
examples, the process 700 may be executed by a software defined radio
(SDR).

[0091] A first signal including a carrier signal modulated with a
non-transpostional modulation (TM) signal is received (702). For example,
the first signal can be a broadcast signal transmitted by a broadcast
transmitter. For example, a broadcast signal can be an AM or FM radio
signal, a broadcast or cable cast televisions signal, a satellite
communication signal (e.g., a satellite television signal, a GPS signal).
In some examples, the first signal is received by a communication device
that includes both traditional and TM receivers and transmitters.

[0092] A frequency of the carrier signal is detected by performing a
carrier extraction process (CAREX) on the first signal (704). For
example, a CAREX process such as that described in reference to FIGS.
3A-4B and 8 can be performed on the first signal to extract the frequency
of the carrier signal from the first signal.

[0093] A TM signal is added to the carrier signal of the first signal to
produce a combined signal (706), and the combined signal is transmitted
(708). The combined signal may be received by various different
receivers, but only TM capable receivers will be able to detect that the
TM signal is present in the combined signal. For example, the TM
modulation signal can be used to carry specialized data for emergency
service personnel. The TM signal can be used to expand the data rate
through a given communications channel during an emergency situation. In
some examples, the TM signal can be used to add supplementary information
to communication signals.

[0094] In some implementations, a TM signal is added to a carrier signal
by modulating a harmonic of the carrier signal (e.g., a third harmonic)
with a data signal. The modulated harmonic is heterodyned to the
frequency of the carrier signal. For example, the modulated harmonic can
be heterodyned to the frequency of the carrier signal by mixing it with
another appropriate harmonic (e.g., a second harmonic) of the carrier
signal. In some examples, a harmonic of the carrier signal is modulated
with data by transposing or time shifting the third harmonic to represent
data from the data signal (e.g., data bits or symbols).

[0095] In some implementations, the phase of the first signal and the
second signal are synchronized before generating the combined signal. For
example, the phase of a TM modulated signal can be synchronized with that
of a received non-TM signal before combining the two signals and
transmitting the combined signal. In some examples, the phase of the
carrier of the TM signal can be phase matched with the carrier signal of
the non-TM signal before the two signals are combined.

[0096] FIG. 8 depicts an example process 800 for extracting a carrier
frequency from an input signal that can be executed in accordance with
implementations of the present disclosure. In some examples, the example
process 800 can be provided as computer-executable instructions executed
using one or more processing devices (e.g., a digital signal processor)
or computing devices. In some examples, the process 800 may be hardwired
electrical circuitry, for example, as an ASIC or an FPGA device. In some
examples, the process 800 may be executed by an SDR.

[0097] A center frequency of an input signal is detected (802). For
example, the center frequency can be detected based on frequency side
lobes of the input signal. In some examples, the input signal can include
the carrier signal modulated with the modulation signal. In some
examples, the input signal is a carrier signal modulated with a
traditional modulation signal and a TM modulation signal. A frequency of
a second signal is detected (804). For example, the second signal may be
the output of a signal generator such as, for example, a VCO or a VCXO. A
difference signal (e.g., control signal) is determined based on the
center frequency of the input signal and the frequency of the second
signal (806). For example, the difference signal represents a difference
in frequency between the center frequency of the input signal and the
frequency of the second signal. In some examples, difference signal is a
DC voltage signal.

[0098] The frequency of the second signal is modified based on the
difference signal to provide the carrier signal of the input signal
(808), and the second signal is outputted as the carrier signal from the
device performing the process 800 (810). For example, a difference signal
can be a control signal for the signal generator and can cause the signal
generator to adjust the frequency of its output signal. The frequency of
the second signal modified until it is matched to the center frequency of
the input signal. In some examples, the frequency of the second signal is
matched to the center frequency of the input signal when the difference
signal reaches a minimum value. In some examples, the minimum value may
be a threshold value indicating that the difference between the frequency
of the second signal in the center frequency of input signal is within an
allowable tolerance. In some examples, the minimum value may be a
magnitude of the different signal voltage that is below the threshold
minimum voltage magnitude.

[0099] FIG. 9 depicts an example process 900 for separating TM signals
from input signals that can be executed in accordance with
implementations of the present disclosure. In some examples, the example
process 900 can be provided as computer-executable instructions executed
using one or more processing devices (e.g., a digital signal processor)
or computing devices. In some examples, the process 900 may be hardwired
electrical circuitry, for example, as an ASIC or an FPGA device. In some
examples, the process 900 may be executed by an SDR.

[0100] An input signal including a carrier signal modulated with a first
modulation signal and a second modulation signal is received 902). For
example, the first modulation signal may be a traditional type of
modulation signal such as, for example, FM, AM, PM, QAM, APSK, etc. The
second modulation signal may be a TM modulation signal. The first
modulation signal is demodulated from the input signal (904). For
example, the first modulation signal can be demodulated using traditional
the modulation techniques. Because traditional demodulation techniques do
not recognize TM modulation, the resulting demodulated first modulation
signal will not include the TM modulation signal.

[0101] The carrier signal is re-modulated using the demodulated first
modulation signal to generate a third signal (906). For example, the
third signal includes an un-modulated carrier signal modulated with the
first modulation signal. The un-modulated carrier signal has the same
frequency as the carrier of the input signal. The first modulation signal
is removed from the input signal by subtracting the third signal from the
input signal (908) to extract the second modulation signal (e.g., the TM
modulation signal) from the input signal. In some examples, the input
signal must be delayed an appropriate amount of time to ensure that it is
in phase with the third signal. That is, due to the demodulation and
re-modulation process the third signal may be out of phase with the
original input signal. Thus, before subtracting the third signal from the
input signal, the input signal can be delayed an appropriate amount of
time. The extracted second modulation signal is provided to a signal
demodulator (910). For example, an extracted TM modulated signal can be
provided to a TM signal demodulator for demodulation.

[0102] While the present disclosure is generally directed to generating
transpostional modulated signals and demodulating transpostional
modulated signals using a third harmonic of a carrier signal, in some
implementations transpostional modulated signals can be generated and
demodulated by using other harmonics of a carrier signal (e.g., a fourth
harmonic, fifth harmonic, sixth harmonic, etc.).

[0103] Implementations of the subject matter and the operations described
in this specification can be realized in analog or digital electronic
circuitry, or in computer software, firmware, or hardware, including the
structures disclosed in this specification and their structural
equivalents, or in combinations of one or more of them. Implementations
of the subject matter described in this specification can be realized
using one or more computer programs, i.e., one or more modules of
computer program instructions, encoded on computer storage medium for
execution by, or to control the operation of, data processing apparatus.
Alternatively or in addition, the program instructions can be encoded on
an artificially generated propagated signal, e.g., a machine-generated
electrical, optical, or electromagnetic signal that is generated to
encode information for transmission to suitable receiver apparatus for
execution by a data processing apparatus. A computer storage medium can
be, or be included in, a computer-readable storage device, a
computer-readable storage substrate, a random or serial access memory
array or device, or a combination of one or more of them. Moreover, while
a computer storage medium is not a propagated signal; a computer storage
medium can be a source or destination of computer program instructions
encoded in an artificially generated propagated signal. The computer
storage medium can also be, or be included in, one or more separate
physical components or media (e.g., multiple CDs, disks, or other storage
devices).

[0104] The operations described in this specification can be implemented
as operations performed by a data processing apparatus on data stored on
one or more computer-readable storage devices or received from other
sources.

[0105] The term "data processing apparatus" encompasses all kinds of
apparatus, devices, and machines for processing data, including by way of
example a programmable processor, a computer, a system on a chip, or
multiple ones, or combinations, of the foregoing. The apparatus can
include special purpose logic circuitry, e.g., an FPGA (field
programmable gate array) or an ASIC (application-specific integrated
circuit). The apparatus can also include, in addition to hardware, code
that creates an execution environment for the computer program in
question, e.g., code that constitutes processor firmware, a protocol
stack, a database management system, an operating system, a
cross-platform runtime environment, a virtual machine, or a combination
of one or more of them. The apparatus and execution environment can
realize various different computing model infrastructures, such as web
services, distributed computing and grid computing infrastructures.

[0106] A computer program (also known as a program, software, software
application, script, or code) can be written in any form of programming
language, including compiled or interpreted languages, declarative or
procedural languages, and it can be deployed in any form, including as a
stand-alone program or as a module, component, subroutine, object, or
other unit suitable for use in a computing environment. A computer
program can, but need not, correspond to a file in a file system. A
program can be stored in a portion of a file that holds other programs or
data (e.g., one or more scripts stored in a markup language document), in
a single file dedicated to the program in question, or in multiple
coordinated files (e.g., files that store one or more modules,
sub-programs, or portions of code). A computer program can be deployed to
be executed on one computer or on multiple computers that are located at
one site or distributed across multiple sites and interconnected by a
communication network.

[0107] The processes and logic flows described in this specification can
be performed by one or more programmable processors executing one or more
computer programs to perform actions by operating on input data and
generating output. The processes and logic flows can also be performed
by, and apparatus can also be implemented as, special purpose logic
circuitry, e.g., an FPGA (field programmable gate array) or an ASIC
(application-specific integrated circuit).

[0108] Processors suitable for the execution of a computer program
include, by way of example, both general and special purpose
microprocessors, and any one or more processors of any kind of digital
computer. Generally, a processor will receive instructions and data from
a read-only memory or a random access memory or both. Elements of a
computer can include a processor for performing actions in accordance
with instructions and one or more memory devices for storing instructions
and data. Moreover, a computer can be embedded in another device, e.g., a
mobile telephone, a personal digital assistant (PDA), a mobile audio or
video player, a game console, a Global Positioning System (GPS) receiver,
or a portable storage device (e.g., a universal serial bus (USB) flash
drive), to name just a few. Devices suitable for storing computer program
instructions and data include all forms of non-volatile memory, media and
memory devices, including by way of example semiconductor memory devices,
e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g.,
internal hard disks or removable disks; magneto-optical disks; and CD-ROM
and DVD-ROM disks. The processor and the memory can be supplemented by,
or incorporated in, special purpose logic circuitry.

[0109] While this specification contains many specific implementation
details, these should not be construed as limitations on the scope of any
implementation of the present disclosure or of what can be claimed, but
rather as descriptions of features specific to example implementations.
Certain features that are described in this specification in the context
of separate implementations can also be implemented in combination in a
single implementation. Conversely, various features that are described in
the context of a single implementation can also be implemented in
multiple implementations separately or in any suitable sub-combination.
Moreover, although features can be described above as acting in certain
combinations and even initially claimed as such, one or more features
from a claimed combination can in some cases be excised from the
combination, and the claimed combination can be directed to a
sub-combination or variation of a sub-combination.

[0110] Similarly, while operations are depicted in the drawings in a
particular order, this should not be understood as requiring that such
operations be performed in the particular order shown or in sequential
order, or that all illustrated operations be performed, to achieve
desirable results. In certain circumstances, multitasking and parallel
processing can be advantageous. Moreover, the separation of various
system components in the implementations described above should not be
understood as requiring such separation in all implementations, and it
should be understood that the described program components and systems
can generally be integrated together in a single software product or
packaged into multiple software products.

[0111] Thus, particular implementations of the subject matter have been
described. Other implementations are within the scope of the following
claims. In some cases, the actions recited in the claims can be performed
in a different order and still achieve desirable results. In addition,
the processes depicted in the accompanying figures do not necessarily
require the particular order shown, or sequential order, to achieve
desirable results. In certain implementations, multitasking and parallel
processing can be advantageous.